@MachtMut
The examples provided are a different medium altogether. CDs, books, magazines etc are physical mediums and steam is for downloaded games not online MMOs.
All MMOs have the same policy about account sharing. Even World of Warcraft has this policy and will most likely not change. There are multiple reasons for not allowing account sharing such as:
- In-game goods being purchased, sold or deleted.
- Account information being changed which will could lead to claims of an account being compromised or "hacked"
- Two or more players fighting over one account which can lead to a long process for the original owner to regain control over said account
- Total loss or deletion of account, character and progress made.
These are just some example but other issues such as account selling, fraud, online harrassmemt, etc can also occur.
As such the above examples are why account sharing in MMOs isn't allowed and won't be changed.